There are three naturally occurring radioactive series - the thorium series, the actinium series, and the uranium series.

有三个天然存在的放射系列，即钍系、锕系和铀系。

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There are three naturally occurring radioactive series - the thorium series, the actinium series, and the uranium series.

有三个天然存在的放射系列，即钍系、锕系和铀系。

youdao